This application claims priority to Korean Patent Application No. 2002-58119, filed Sep. 25, 2002, in the Korean Intellectual Property Office.
1. Field of the Invention
The present invention relates generally to a radio communication system and, more particularly, to an apparatus and method for receiving radio frequency (RF) signals by which sensitivity degradation due to 1/f noise can be minimized.
2. Description of the Related Art
In order to satisfy continuous demands on multi-functional, high-performance radio frequency (RF) communication services and to facilitate highly integrated, smaller sized and more energy efficient communication systems, a direct conversion type receiver as shown in FIG. 1 has been widely used as a RF receiver in recent RF communication systems. The direct conversion receiver includes a pre-processing unit 10 for band-pass filtering an input RF signal received through an external antenna ANT, a mixer 20 for mixing the input RF signal with a local oscillation signal LO, and a baseband processing unit 30 for providing a baseband output.
In such a direct conversion receiver, an input RF signal is affected by noise having a frequency characteristic as shown in FIG. 2, e.g., 1/f noise, if the input RF signal is lowered to be within a baseband through the mixer 20. The direct conversion receiver is greatly affected by 1/f noise, which is inversely proportional to the frequency of a signal in the baseband. Particularly, in the case of implementing the direct conversion receiver with CMOS technology, a frequency roll-off as shown in FIG. 2 increases to an order of a few mega-hertz (MHz) and an effect due to 1/f noise becomes significant. Further, due to such 1/f noise, the sensitivity of the receiver is considerably degraded. Such sensitivity degradation of the receiver causes more serious problems in a narrow band system such as a GSM system and, therefore, conventional narrow-band direct-conversion receivers have not employed CMOS technology. Therefore, a need exists for utilizing CMOS technology to realize highly integrated, smaller sized and more energy efficient receivers in narrow band communication systems.